Installation is stuck at 95% "moving items into place".

I have been trying to install this update, but each time, it stops at about 95% by "moving items into place" and is stuck. This has been happening with every update Apple has come out with since I've gotten the computer. In July, I had to wipe my hard drive in order to install the update, then put my data back on via Time Machine.

The installation always sticks at 95% while "moving items into place" and then will go no further. I have to manually shut down the computer which usually results in my computer not functioning properly or not starting up at all. This time, after getting help from the call center, I managed to get my computer to start again, but the installation still did not work. I tried it again and once again it froze at 95%. After manually shutting down, my computer did start up again as normal (although I'm still a bit nervous about finding some sort of major problem where I least expect it...). I've run Disk Repairs and all seems to be in order. The update still did not install.

I'm just afraid to try to install the update again...what can I do? And should I wait to update my iPhone software as well until I do this OS X update?

Thanks for any help you can give me!